Process for extraction of hydrocarbons



Patented Aug. 14, 1945 i UNITED sTATas PAT NT zssaila OFFICE PROCESS FOR EDI TRACTION OF HYD CARBON Charles E. Welling, Okla assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing; Application September 5.1m,

, Serial No. saws-1..v

3 Claims. (01. 260-4815);

My invention relates to an improved process for separating the components of a hydrocarbon mixture. More, particularly, it relates to a,

method of concentrating conjugated dioleflns.

Still more particularly. this invention relates to a, process of liquid-liquid extraction in which a hydrocarbon mixture containing aliphatic or alley-1" clic parafllns or olefins and alicyclic or aliphatic dioleflns, usually conjugated, generally closeboiling and generally of the same number of car-- bon atoms as the olefin, is contacted with a suitable selective solvent-in order to separate said hy-.,

v drocarbon mixture into fractions of unlike composition oriproperties, Still-more particularly it relatesto such a process wherein the hydrocarbon stream being extracted consists of aliphatic or alicyclic mono-oleflns and aliphatic or alicyclic conjugated dioletins both of which have at least four and notmore than seven carbon atoms in the molecule. Still more specifically it relates to, the separation of aliphatic conJugated penta-- dlenes. especially isprene,- from close-boiling 1 pentenes, especially low-boiling pentene-Z, and of However, it may.

butadiene from butene-l. equally be. applied to the separation of cyclopentadiene or piperylene from cyclopentene.

'In another aspect the inventionrelates to an improved method of separating mono-olefins from close boiling diolefins by a novel series of steps comprising selective solvent extraction us-g ing a low-boiling. selective solvent which preferentially dissolves the [diolefln andwhich also forms a constant-boiling mixtureor azeotrope with the mono-olefin, whichareotrope boils well' below the diolefln or azeotrope with the diolenn, and fractional distillation of the extract phase enriched in dioleiln but also carrying some monoolefln to remove themono-olefln overhead in the form of an azeotrope with the entraining agent. In this way the overall separation of diolefln from mono-olefin is greatly enhanced without requir v ing the excessive consumption of heat in the fractionating column and fractional distillation load that would be entailed were the entire original feed passed directly'to an azeotropic distillation step. If desired, the rafilnate from the extraction zone may similarly be subjected to such a azeotropicdistillation step. a

.dlolefln mixtures.

At the present time there are various processes, such as thermal cracking and catalytic dehydrogenation, that areemployed for treatinghydrocarbons to yield as products mixtures of one or more dioleflns together with other hydrocarbons,

. such as olefinsr It is of considerableimportance about an equally small temperature interval sepzarates the boiling points of isopreue and the lowboiling isomer ofpentene-2. Because of such small boiling point difierences, it is obviously difflcult if not impossible 'to separate byfractional distillation certain hydrocarbon mixtures that contain dioleflns together with close-boiling hydrocarbonsoi other types; i i

It is known toemploy certain selective solvents to treat liquid hydrocarbonmixtures in order to eflect more or less complete separationof the differenttypes of hydrocarbons containedtherein.

Thus, selective solvents such asTJhlorex" (2,2'-

dichloroethyl ether), nitrobenzene, phenol, turfural, and dlmethyl formamide have-been used in they selective extraction of "lubricating oil stocks in order to extract naphthenic and aromatic types of hydrocarbons andto produce asrafllnate lubricating oils of highly paratllnic character. It is By ,close-boilinge" as used herein, I mean so close in boiling point as to make separatio'nby simple fractional distillation impossible or uneconomical because requiring an excessive number of furtherknown to employ selective extraction to,

recover a mixture of oleflns and dioleflris from cracked gasolines or refinery gases. It also has been proposed to separate oleflns. and dioleflns contained in liquefied normally gaseous hydrocarbon mixtures by liquid-liquid extraction.

However, there is a serious ldifliculty encountered in practicing liquid-liquid selective extractionof olefin-,diolefln mixtures, particularly when the hydrocarbon mixture is composed of hydrocarbons having not more than seven carbontatoms per molecule. In general, the intersolubility of the lighter oleflns and diolefins'with the usual selective solvents is sozr'eat that itis necessary to resort to reduced temperatures in order to maintain two liquid phases. It is,-of course, necessary ior liquid-liquid extraction that two liquid phases exist and :that the-extraction system be plates. This term denotes hydrocarbons boiling ithin three'degrees and usually within two srees of one another.

'maintained at a-temperature below the miscibility temperature for the hydrocarbon mixture and the solvent. In order to operate at temperatures below the miscibility temperature of mixtures comprising three and four carbon atom hydrocarbons, it has been proposed to operate an extraction process at temperatures as low' as 60 F. However, the excessive refrigeration costs involved have prevented commercial utilization of; such a process.

The principal object of my invention is provide an improved process for the separation of a liquidor liquefied mixture of oleflns and dioleflns by selective extraction with a selective solvent. It H is a further object of my invention to provide af process for the separation of a liquid mixtureof olefins and dioleflns by selective extraction with a solvent at temperatures higher than those that it has heretofore been possible to employ. An-

: other objectof my invention is to provide a proc j ess for the separation of close-boiling mixtures of olefin and diolefln hydrocarbons that boil within or below the boiling range of gasoline, by selective extraction with a selective solvent. It is another,

I object of my invention to provide a process for the selective extraction of mixtures of olefins and tial boiling point is at least 175 C. and usually 215 C. or higher and the average molecular weight is usually at least 200; While a parafllnic oil of the nature of mineral seal oil or white mineral oil such as that known as NujoP' is preferred, I may use a somewhat lower boiling essentially paramnic material such as kerosene which is substantially vention, I may employ contacting means such as rnixers and settlers or packed or unpacked towers through which the selective solvent and mixture being extracted are passed, either concurrently or,

preferably, countercurrently.

1 The pressure'at which it will be necessary to 1 work, in practicing rim-invention, will depend dioleflns whereby'a group of materials that have heretofore been considered unsuitable-for'use as. selective solvents may be advantageously 'used. Still another object of my invention is to provide a process for the selective extraction of mixtures of olefins and dioleflns at temperatures that are commerciallyfeasible while employing as selec-;-

tive'solvent some one of the group of materials;

upon the hydrocarbon mixture tobe treated, the

selective solvent chosen, and the temperature at which the process is operated. In any event, the

' pressure should be sufllcient to maintain the mate- 1 7 that are suitable for use as entraining agents in the separation by azeotropic distillation of closeboiling. mixtures of olefinand diolefin hydrocarbons. It is a further object of my invention to provide a process whereby a mixture of close-boil- 1 ing olefins and dioleflns are subjected to selective extractionnat atemperature above that'whichf might be employed in known processes, followed by azeotropic fractionation of extract or raifinate,

or both, with the same material employed both as' selective solvent in the extraction and as entrainrials in" the liquid phase. The temperature at'which the liquid-liquid contacting according to my process is carried out will vary, depending upon the composition of the hydrocarbon mixture to be separated, the amount of high-boiling diluent that'is added tothe hydrocarbon mixture, the particular solvent employed, and the ratio of solvent volumeto volume of the hydrocarbon mixture before addition of diluent;

"Usually the temperature will range from about 0 C. to about room temperature, though it may be higher-than room temperature up to'iust' below the temperature of miscibility. My processdiifers from known methods i'nthat by the addition of a ing agent in the azeotropicfractionation: Other objects will become apparent from the following description of my invention. 7 s

I have now found that an extraction of a mixture of olefins and dioleflns with a selective solvent may be practiced in a higher and more con: venient temperature range if the mixture of hy-- drocarbons to be extracted is first diluted With a high-boiling, preferably paraflinic type, oil that is free from double bonds and has low solubility in suitable diluent to the hydrocarbon mixture I am able to operate my process ata temperature level above the minimum temperature at which omthe selective solvent employed. The solution thus obtained is contacted with the selective solvent .to'extract the diolefin preferentially. .In this manner I have succeeded in carrying out extrac- I tions at or near room temperature, wh'ereas con-' siderably lower temperatures would have been necessary in: order to attain the same result by known methods. I

The diluent employed according to process may be a mineral seal oil or refined white mineral oil or some similar material preferably essentially parafflnic in nature. j'The'; diluent may consist q either of a siiigleTco'mpound or may be amixture.

. The diluent must possessaboillng point considerably higher than the boiling points of the principal components of the hydrocarbon mixture to be extracted so that it is readily separated therefrom by stripping or fractional distillation. Ordinarily its boiling point is so high that it maybe readily? separated from the solvent in the'zsame -manner.

In general the diluent is a high-boiling hydrocarbon oil consisting essentially of paraflin hydrocarbons rangingv upwardly from decan'e. Its iniplete miscibility'of the hydrocarbon mixture and the solvent would occur if the solvent and the hydrocarbonmixture were to be brought together in the sameratio'as that employed in the extrac- I tion according to myproces's. The maximum temperature at which my process may be operated will lie below the critical solution temperature of the mixture of solvent-,'h'ydrocarbon mixture, and added diluent; The exact value of this maximum temperature for operation is dependent upon the amount and character of high-boiling diluent that is added to the mixture-of olefin and diolefln hydrocarbons, but it can be readily determined by trial for any particular case.

I may utilize known procedures in handling the extract and raflinate phases resulting from practicing my processfln' general it will be necessa'ry to treat the raffinate phase in such a manner as to removeany suspended or dissolved solvent and also to effect a separation of high-boiling diluent from the rafilnate; thefhigh-boiling dilu- "ent may then, of course, be "r'ecycled to the extraction unit. Depending upon the particular solvent, such methods of separating the dissolved solvent from the hydrocarbon mixture as waterwashing 0r fractionation maybe used. Similar methods of separation may be employed in treating the extract phase torecover the solvent and any high-boiling diluent, whichmay berecycled to appropriate points in the extraction unit, and the diolefln-rich hydrocarbons recovered from seed-,1 i A the extract phase may be withdrawn as a product of theprocesae It is generally possible and convenient so to choose the solvent and the high-boiling diluent in any specific case that a considerable diiference lation are available, such as cooling and separation ofv phases, water washing, steam distillation,

and the like.

The selection of suitable relative proportions of high-boiling diluent tothe mixture of hydrocarbon to be separated will be well within the skill of the art inthe light of this disclosure.

These proportions may var over awide range but will frequently involve about equal amounts by volume of the hydrocarbon mixture, i. e. the oleiln-dioleiln mixture, and the diluent. Usually the amount of the diluent will be within the range of from about 50% to about 200% by volume I based on the volume of hydrocarbon mixture.

' Likewise the selection ofextraction conditions of ressure, temperature, selective solvent, em ployed, diluent employed, and ratio of solvent volume to the volume of hydrocarbon mixture and consequently tothe volume of the hydrocar bon'mixture plus high-boiling diluent are matters well within the skill ofworkers in the art in thelight oi the teaching herein. It will be obvious that all of the factors and variables involved are largely inter-related with each other The selective solvents lust enumerated are with the exception of sulfur dioxide relatively highboiling, that is,'b oiling atfrom 100 to250' C. at atmospheric pressure which it is preferable to employ for extraction withsuch solvents.

As will beiobv'ious, the hign-boum penmmc diluent remainsin the raflinate phase.

" "In'certaincases' 1 havefound it desirable to boiling compounds of carbon, hydrogen, and oxyemployas the selective solvent a material chosen from I a group'consisting of water-soluble lowgen boilingbetween' and 65 Cfthat I have found to be desirable entraining agents for the aaeotropic fractionation of'close-boiling mixtures of the lower oleflns and dioleiinsand also satisfactorily selective for dioleflns as against monoolenns or paramns. This group of compounds consists of acetaldehyde, 1 propionaldehyde, 1 propylene oxide (1. 2), methylformate, and methyl alcohol. By the 'useof a. comp nd chosen from this groupas'a selective solvent 'in'an extraction process according to my invention, followed by azeotropi'c fractionation of either the extract or ramnate or both with'the same compound as an entraining agent, I have found it. possible to obtain excellent separations of olefin-diolefln mixtures while'realimg simplifications and econ- 'omies' in-design and operation. Flor-example, by

my'process it'is possiblejtofemploy compounds from this group as selective solvents'for the extraction of mixtures of olefins anddioleflns containing from four to about seven car on atoms per molecule at temperature levels easily. and in- I 'expensively attained, whereas conventional extractions-with the same compounds assolvents and that when one condition is changed adiustment of one ormore others frequently is necessary. The relative proportions of solvent and low-boiling lxvdrocarbon mixture may vary widely, depending upon the concentration of dioleiln in said mixture and upon other factors-as well.

Ordinarily I use'the solvent in an amount rang ing from 25% to 300% by volume based on the volume of said mixture. 7

As will be obvious, the concentration of diolefln to be extracted in the hydrocarbon mixture being treated will vary within extremely wide limits say from about 1% to about by volume. As

the selective solvent I prefer to use any known -and' the "same hydrocarbon mixtures as. charges would necessarily have to be practiced at undesirably low-temperatures on'account of the high mutual solubility offthesolvents' and the hydrocarbons involved.

The" groupof f selective: solvent-entraining agents enumerated in thepreceding paragraph have in common the propertiesthat they are good selective solvents for diolenns are good entraining agents, that dswithhirdmcarbons they form azeotropes boiling at progressively higher tion' sothat' theazeotrope with para-mus comes temperature withincreasing degree of unsaturaoverhead before'that with olefins or diolefins and organic solvent which is essentially immiscible with or a non-solvent of paraflins and which dissolves dioleflns preferentially with respect t2.

mono-oleilns or parailins. Examples of typical solvents are: the n, n-substituted dialkvl fatty acid amides such as dimethyl formamide, diethyl the azeotrope with mono-oleflns boils markedly 'lomver than that with dioleiins, with the result that ready separation by fractional distillation a is effected. In addition, they are sufliciently waformamide, etc., aldehydes such as benzaldehvde,

furfural, etc., nitrobenzene, aniline, fur'furyl alcohol, furfuryl amine, Chlorex," phenols such as phenol (preferably in admixture with water), cresol, cresylic acid, resorcinoi, etc., ethylene chlo- 1 comprise theCaand C: saturated aliphatic aldeerohydrin, esters such as benzyl acetate, phenol.

acetate, methyl furoate, Y etc.

In general the solvent should be inert andform I no compound or addition product with the othercomponents present; Liquefied sulfur dioxide is j generally unsatisfactory because of its marked tendency to combine with the dioleilns to form a monosulfone addition compound. However, if conditions preventingor inhibiting this forma. tion are employed or if formation of the monosulioneis not objectionable, liquid sulfur'dioxide may be employed as the selective solvent.

ter-soluble that theycan be readily separated from hydrocarbonsby water-washing. which is a necessity in commercial operation. Furthermore they are the only compounds that I have found to m'eetthese requirements" in an exhaustive series of-tests. .-In' addition they are'ailf-organic I compounds containing on]? i bon hvd 'sen and oxygen and boiling between 20 and 6550. They hydes (formaldehyde is wholly unsatisfactory), the lowest saturated aliphatic alcohol, the lowest alkyl' ester of the lowest fatty acid, and the lowest alkyl substituted derivative of the simplest alkylene oxide. Thus,'t,he fl ve compounds set forth form a natural grouping meeting certsinpeculiar requisites and having "a commiu'nity of'physical and chemica i s-.1 l

Inwroceeding n il fim ment Just describedpthe extraction step itself may be conducted in the same manner de'scribed above when using the high-boiling solvents. Following the extraction the extract and the rafdrocarbom iinate phases are separated from one;another in the conventional manner. Either-or both is then fractionally distilled to separate asan overhead j the lowest-boiling azeotrope. If the amountof selective solvent in the ,feed to the distillation step'is insumcient to form an azeotrope with all of the less saturated component of the phase,

I may introduce suillcient entrainin'g' agent, a usually identical with the selectivevsolvent 9.1-. readypresent, to makeup this deficiency. It is usually preferred, however, to use enough of the,

selective solvent in question in theextraetion step to function as the entraining agent for all the hy drocarbons sought to, be separated-inthe subsequent azeotropic distillation ofat least'the extract phase and, if desired, theraflinate phase as well.

Upon Ifractional fraction is the azeotrope with any low-boiling (C4 to C7) paraflin present, and thenext fraction is the azeotrope with any monoolefin present.

7 The next fractionmay be the azeotrope with the diolefin. r dependingon the amount of entrainer present'and the wishes of the operator,

thediolefin may simply form the kettle product,-

or be partially removedas aside-stream or overhead, the balancebeing removed as kettle prod y ucti Obviously thefractions referred to may be taken off either as successive overhead fractions or as aplurality of sidestreams.

Likewise, upon fractional distillation of the rafflnate, the fractions recoveredwill depend on the composition of therafllnate onwhether or not additional entrainer is.added,; and on the boiling hydrocarbons to be resowed are dissolved in the high-boiiing-diiuentprior to con- I tacting, I need-not proceed: in'this way but may instead contact the three materials -hydrocar-- bon mixture, high-boiling I diluent and selective solvent-with one another in any way, by which the desired equilibrium is obtained: --Thus, I may distillation of thehextract, which is'e'nriched in dioleilns, the lowest boiling contact the :hydrocarbon mixtureiiwith a pre-' formed mixture ofthediluent and solvent, or indioleflns.- My process is also applicable to the separation of cyclic oleilns from diolefins and to the separationofparamns from dioleflns.

My invention may befurther illustrated and described bythe following specific examples.

' I Example I l e In preliminary experiments it was found that f at room temperature pentene-2(n 3-1.3793) and isoprene (11 1.4210) were each completely miscible with dimethylformamide when one volv ume of hydrocarbon was contacted with about an wishes of the operatonfIn ,mostcases the ratfinate will contain substantial amounts of dis 1 V solved selective solventwhich will form azeotropes with any'low-boiling parafiin present, any

mono-olefin-present, and any diolefln present, and these will come over in the ordennamed until all of the azeotropes have, been removed. The solvent will notordinarily form an azeotrope with the high-boiling paramnic diluent employed and may beseparated therefrom by simple distilla; tion. OrJthe solvent and diluentmay be simply not separated andmay be recycled as such to.

contact with the olefin-diolefin mixture to be ex,

equal-volume of dimethylformamide. '.A single batchwise liquid-liquid extraction was then carried out at room temperature, whereby 35 volumes of a mixture fpentene-Z and'isoprene in about I equal volumestogether with-.35 volumes of a white mineral oil wa :haken with 35 volumes of dimethylformam ide. ,After separationof solvent (or, extract) and hydrocarbon v(or ramnate) phases, each phase wasi'reedof isolvent. by water- Washing, and the ,olefin and diolefln hydrocarbons were recovered from the water-insoluble 1 residues by distillation. The results obtained in tracted. Ordinarily the amount of solvent dissolved in the raffinate phase will be fairly small. When in the distillation of the raflinate, the

amountof solvent present :to act as entraining, agent is insufficient to formazeotropes with the light'hydrocarbons present,;these may be re-' movedby simple distillation or stripping after,

any azeotrope or azeotropes have been driven off.

Thus, any residual parailin,- mono-olefin, or diolefin and mixtures thereof .are readily removed but such mixtures are not recoverable as separate fractions. As will'beobvi'ousfrom' the foregoing,

it is ordinarily preferred to finallyresolve the 7 1 isoprene lviatenal I Volumes ll by "D" v Percent Light hydrocarbon charge 3 35. 0 1.3994 48. 2 ,Li htv hydrocarbons from solvent 1 Y extract) phaseu 10.4 1.4035 58.0 Light hydrocarbons from hydrocarbon (raifinate) phasc 19.0 1.3970 42.4 Light hydrocarbon loss i 5. 6

this'extraction are summarized as'follows:

Itis readily seen from these'da'ta that a very conside rable separation, of isoprene from the origina1 mixture of isoprene and pentene-2 was effected by. this single extraction with dlmethylformamide as the selective solvent. Furthermore,

several azeotropes obtained by the distillation of the extract phase and/or the raflinate phase by water washing which dissolves the'solvent away from the purified more or less concentratedhy- It isjpossible to operate in such manner that theiraflinate is entirely free of diolefin or that vthe extract is entirelyffree'of monooiefin, as will be obvious to those skilled in the art. In such case the other phase will ordinarilycontain a higher proportion of the component other than the one sought to be concentratedtherein.

- While. inthe foregoing detailed description," there is described a method vwherein the lowthe extracti'on'was carried out-at'a temperature such that no cooling or refrigeration was required. As shown by the preliminary experiments, it would nothave been possible to have performed the extractionatthis temperature by the use of known methods of operation. ample the great practical value of my process is readily perceived. A much more. complete separation of olefin and diolefin would have'been effected by repeatcdextractions orbycontinuous counter-current operation. v,

' Example 11 i In preliminary experiments it was found that both pentene-2 and isoprene were completely miscible with acetaldehyde down-to about -75 C.

From this exaseano A single batchwise'liquid-liquid extraction of a mixture of these hydrocarbons was then carried out according to this invention at the temperature of melting ice with acetaldehyde as the selective solvent. The mixture of pentene-z and.

isoprene consisted of about 50 volume per cent pentene-2 (1th 1.3794) and 50 volume per cent of an isoprene concentrate (11 1.4202) that contained about 96.5 per cent lsoprene; the .refractive index of the mixture was 1.3999, corresponding to a calculated isoprenecontent of 48.6 per cent, assuming the refractive index of pure isoprene to be 1.4216.

In the extraction, a mixture of 25 volumes of the oiefin-diolefin mixture plus 25 volumes of a high boiling white mineral oil was contacted with 25 volumes of acetaldehyde. After separation of solvent and hydrocarbon phases, the upper or solvent phase was washed free of acetaldehyde with water, and the olefin-diolefin mixture contained in the residue was separated mm the residual mineral oil by distillation. The lower or raffinate phase was first distilled to separate acetaldehyde and the light hydrocarbons from the residual mineral oil, and then the light hydrocarbons were freed from ,acetalidehvde by water-washing. The results are summarized in the following tabulation.

The loss of 4 volumes of light hydrocarbons was largely occasioned by their rather high volatility and by the opportunities afforded for vaporization during the various operations subsequent to the extraction proper. Losses from these causes would be greatly minimized by commercial scale operations in closed systems. The same is true with regard to the loss shown in Example I. d

It is seen fromthe tabulation that the single stage of extraction effected a considerable separation of isoprene from pentene-2. This separation would be increased to any desired degree by further extractions. Of particular importance is the fact that by the addition of mineral oil the essential condition for such extraction, that is, the existence of two liquid phases, was maintained at a readily accessiblev temperature level 7 much above the temperature level that would amounts of refrigeration. In fact it enables the separation to be carried outv at ordinary atmospheric temperature. It provides an improved method of recovering C4 and Cs diolefins from their respective streams. In the preferred mOdi-J fication using the combined solvent extraction, and azeotropic distillation, the same low-boiling organic compound performing the dual functions of selective solvent and entraining agent, additional advantages are attained among which are the simplification of the combined steps, easiercontrol, and better overalljseparation. Accordingly it will be seen that the process described herein is a very valuable contribution to theart of diolefln separation and concentration.

Because the invention may be practiced otherwise than as specifically shown herein, and because many modifications and variations of it will be apparent to those skilled in the art, it should not be restricted except as specifically indicated in the following claims.

I claim:

1'. A process of concentrating a conjugated diolefin of from four to seven carbon atoms per molecule from a hydrocarbon mixture consisting of said diolefin and a close-boiling olefin of the same number of carbon atoms per molecule which comprises diluting said mixture with a high-boiling paraffinic oil free from double bonds and having an initial boiling point of at. least 175 C. and an average molecular weight of at least 200, extracting the resulting diluted mixture with-a selective solvent which is preferential for said diolefin, which solvent is inert to-- wards the components of said diluted mixture, is, substantially a non-solvent for said oil, is a water-soluble organic compound containing only carbon, hydrogen and oxygen, boils between 20 and C., and forms with .said olefin an therein as .azeotropic entraining agent,- and thereby effecting separation of the olefin content of the extract from the diolefin contentv thereof, said solvent being used in said extract ing step in amount at least sufllcient to form an azeotrope' with all of the olefin content of said extract. I v

2. The process of claim 1 in'whichsaid'diolefin is isoprene and said oleflnis pentene-2.

3.The process of claim 1 in which said solvent is acetaldehyde.

CHARLES E. WELLING. 

